The present invention relates to multi-piece fasteners and more particularly to a high strength blind bolt using a lockbolt like swaged construction and providing a high final clamp load of workpieces secured together and further relates to such blind fasteners particularly adapted for constructions utilizing box beams or columns, bridges and the like.
The present invention relates generally to multi-piece blind bolt fasteners which include a main sleeve, an expandable sleeve and a pin wherein the expandable sleeve is moved axially relative to the main sleeve and is expanded radially thereover in response to a relative axial force applied via the pin. In this regard the blind bolt of the present invention bears a general resemblance to a threaded blind fastener of the type shown in U.S. Pat. No. 3,643,544 issued Feb. 22, 1972 to Joseph H. Massa; fasteners of this type have been sold under the trade name Visu-Lok and/or Jo-Bolt by the Voi-Shan Manufacturing Company of the United States. See also U.S. Pat. No. 3,262,353 issued Jul. 26, 1966 to R. Waeltz et al, U.S. Pat. No. 2,765,699 issued Oct. 9, 1956 to J. LaTorre, U.S. Pat. No. 2,887,003 issued May 19, 1959 to Brilmeyer and U.S. Pat. No. 3,107,572 issued Oct. 22, 1963 to Orloff.
In the present invention the high strength blind bolt includes a collar which cooperates with the pin in the manner of a swage type fastener such that, after the blind head has been formed, the application of a relative axial force of increasing magnitude between the pin and collar causes an installation tool to swage the collar into lock grooves in the pin. In this regard U.S. Pat. No. 2,114,493 issued Apr. 19, 1938 to L. C. Huck and U.S. Pat. No. 2,527,307 issued Oct. 24, 1950 to L. C. Huck generally show a swage type connection between the pin and sleeve of a blind fastener.
The high strength fastener of the present invention can advantageously utilize the collar design of U.S. Pat. No. 4,921,384 for Swage Fasteners With A High Stand-Off Collar by Keith Nordyke and issued May 1, 1990. In addition the present invention could utilize the groove shape and concepts of U.S. Patent application Ser. No. 185,327 by Richard D. Dixon for High Strength Fastener and Method filed on Apr. 20, 1988. All of the above patents and noted patent application of Dixon can be considered as prior art relative to the present invention.
The high strength fastener of the present invention includes a pin, an expandable or primary sleeve, a main or secondary sleeve, and a collar adapted to be swaged into lock grooves in the pin in response to a preselected relative axial force applied between the pin and collar. In the present invention the collar initially transmits an axial force from the swage anvil of the setting tool to the main sleeve. The pin has an enlarged head which transmits an opposite axial force against the expandable sleeve by virtue of a pulling force exerted by the tool. As the axial force increases the expandable sleeve is moved axially relative to a tapered nose portion at the blind side of the main sleeve and is radially expanded to overengage that end of the main sleeve. The axial movement and radial expansion of the expandable sleeve continues until the resultant blind head is moved into engagement with the blind side surface of the workpieces to be fastened. Now the workpieces are pulled together by the further application and increase in the relative axial pulling force. The force clamping the workpieces together continues to increase until the collar is swaged into the lock grooves on the pin. The final clamp load on the workpieces can be determined first by an initial magnitude of relative axial force attained just before the collar starts to be swaged onto the pin and thereafter by elongation of the collar in response to swage. The initial axial clamp force on the workpieces is sometimes referred to as "pre-load" while the final clamping force after full swage is referred to as "final clamp load". The beginning of swaging at this pre-load is sometimes referred to as "primary clinch".
The high strength blind bolt of the present invention is adapted for use in applications in which high strength bolts, such as SAE Grade 5 (ASTM A325) or higher, are frequently used. It is also desirable for use where blind welding, nut plates and other complex construction fastening systems are used. In this regard, the blind fastener of the present invention is especially suited for construction of buildings, bridges, and the like where high strength and durability are of considerable importance along with the capability of providing high clamp loads of the assembled parts. Thus the blind bolt of the present invention has a high tensile strength such as SAE Grade 5 or greater and/or the tensile strength of the Japanese Grade F8T bolt or greater. This is accomplished, in part, by the use of high strength ferrous materials having a high hardness. With such materials, factors such as notch sensitivity, stress corrosion and the like can become more significant especially with a pin of high hardness. In the present invention these factors are addressed by a unique balancing of the strengths, materials and configuration of the individual components. In addition the effects of stress corrosion on the high hardness pin are inhibited by self sealing features protecting the highly stressed portions of the pin from exposure and/or access to the atmosphere.
Thus in many applications it is desirable to provide a high level of final clamp load in the fastened joint. This can be a problem unless a blind head is formed which will retain its integrity in response not only to a pre-load of high magnitude but also to the subsequent desired final clamp load. Thus in the present invention it is also desirable that a high strength blind head be formed to sustain the high pre-load and subsequent high final clamp load. But this poses an additional problem since the application of the necessary relative axial force of substantially high magnitude to attain the high pre-load requires the collar to have a high hold-off capability to resist the initiation of swage. In these cases the relative geometries of the swage anvil and engaging end of the collar are selected to provide hold-off or stand-off of initial swage until the desired pre-load value is attained.
The blind bolt of the present invention utilizes the unique collar construction of the '384 Nordyke patent (supra) for providing a blind bolt swage type fastener having a high stand-off capability while providing generally equal groove fill in the pin and minimizing localized pin distortion.
In one form of the invention, the wall thickness of the expandable sleeve is maximized to thereby increase the strength of the formed blind head. As will be seen, this is accomplished by a unique assembly and manufacturing procedure.
In some applications it may be desirable to provide a pin and collar combination in which there is a predetermined amount of "overpack". Overpack occurs where the volume of collar material to be swaged in the pin lock grooves is greater than the available volume defined by the confronting volume of the cavity of the swage anvil and the pin lock grooves. The pin and collar construction of the present invention provides for a more uniform overpack condition over its swageable length.
In one form of the invention, the lock grooves of the pin are in the form of a helical male thread. In such case the collar can be provided with a mating, female thread of a preselected extent such that the initial pre-assembly of the fastener components can be accomplished. The female collar thread is selected such that, in response to the relative axial force and at a level prior to the initiation of collar deformation or swaging (primary clinch) into the lock grooves of the pin, it will shear or deform such that the collar will be free to move axially over the pin and to respond to the installation loads in the same manner as a collar without such female thread form. In this regard a construction could be utilized such as that shown in U.S. Pat. No. 4,867,625 by Richard Dixon for Variable Clamp Fastener and Method issued Sep. 19, 1989. Similarly, a construction could be used such as that shown in the U.S. Patent to Walter Smith U.S. Pat. No. 4,813,834, issued Mar. 21, 1989. Both of the latter patents can be considered as prior art to the present invention.
In some applications it is desirable that the fasteners have a high strength, high performance characteristic both in clamp up and in fatigue. In this latter regard then, it may be advantageous to utilize the groove shape and concepts of the invention of the '327 application of Dixon.
Thus, in one form of the present invention, the lock grooves in the pin are very shallow and are constructed to have roots of a simulated streamlined shape. The lock grooves are helical and define a desired thread configuration. The shallow grooves and simulated streamlined shape, however, provide a resultant fatigue life which is superior to that of a comparable threaded fastener. Since the preceding construction is shown and described in the noted '327 application of Dixon and since the present invention is not restricted to such a construction the details thereof, while incorporated by reference, have been omitted for purposes of simplicity.
The high strength fastener of the present invention may be utilized in applications where the hole sizes in the workpieces may be somewhat oversized or in applications where the material at the blind side of the workpieces is relatively soft and subject to deformation. Another form of the invention addresses such conditions by using an additional sleeve having a relatively thin wall and hence which is adapted to readily collapse around the blind side opening to thereby inhibit movement or extrusion of the expansion sleeve into an oversized hole and/or inhibit deformation of the blind side surface of a workpiece made of a soft material.
Thus it is a general object of the present invention to provide a novel high strength blind bolt having a swage type construction.
It is another object of the present invention to provide a unique blind bolt construction for forming a high strength blind fastener having a high strength blind head.
It is still another object of the present invention to provide a unique blind bolt construction for forming high strength blind fasteners having a high strength head and including a swage type construction utilizing a collar having a high stand-off capability.